1. Field of Invention
The present invention relates to an apparatus and a method for driving fans, and more particularly, to an apparatus and a method for identifying and driving different fans when coupled to a computer system.
2. Related Art
Currently, various components configured on a mother board would generate heat when operating, especially for those high-performance computing systems. Although some new heat-dissipation systems such as liquid cooling systems are available for specific applications now, conventional fans are still much more common in computers.
Generally, a fan has a power connector for connecting to a receptacle on a mother board, thereby utilizing electricity from a computer system and operating under system control. Two common types of the power connector are for receptacles that have 3 and 4 pins respectively, which are so-called 3-pin fan (as shown in FIG. 5A) and 4-pin fan (as shown in FIG. 5B). The receptacle 410 for the 3-pin fan has a ground pin Jg, a power pin Jp and a speed detection pin Jd, and the one for 4-pin fan has the fourth speed control pin Jc. Correspondingly, the power connector of a 3-pin fan has a ground contact, a power contact and a speed detection contact, while in a 4-pin fan the power connector has an additional speed control contact except the former three ones. Other differences for 3-pin and 4-pin fans are control circuits and control mechanism.
In the prior art, both 3-pin and 4-pin fans receive power (electricity) via the power contacts. To provide corresponding heat-dissipation performances under different system temperatures, the fans need to operate at corresponding speeds controlled by the computer system.
The 4-pin fan has the dedicated speed control contact for speed control, while the 3-pin fan uses the power contact to control speed. Most computer systems input pulse width modulation (PWM) signals to the speed control contact of the 4-pin fan, which is capable of control fan speed without effecting power supply through the power pin. However, for the 3-pin fan, the PWM signal is input to the power switch 420 to control the power switch to remain ON during the time period. Thus, the time period of power inputting through the power contact is controlled. So does the speed of the 3-pin fan.
Comparing to the continuous power supply mechanism of the 4-pin fan, aforesaid intermittent mechanism substantially influences the operation of the 3-pin fan and makes the speed control unstable. Except the duty cycle of the PWM signal is 100%, other duty cycles have a time period that the power switch is OFF, which means the 3-pin fan will be lack of electricity to output speed signals “Tachometer” through the speed detection contact of the power connector and the speed detection pin of the receptacle. Meanwhile, a hardware monitor controller will fail to obtain correct speed from output speed signals. In fact, the difference between the speed obtained by the hardware monitor controller and the real speed of the 3-pin fan could be 2 times. Accordingly, the 3-pin fan cannot reach a given speed responding to a specific system temperature, or remain at the same speed. The system components, consequently, are easily over-heated and damaged. Certainly it is the same for the 3-pin fan.
However, considering cost and system demands, the 3-pin fans are still very useful. For the two types of fans with different specifications and different control mechanisms, no computer system in the prior art is capable of identifying and driving the two fans, neither to provide a interface for both fans.